The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Moving Picture Experts Group (MPEG) and Video Coding Experts Group (VCEG) have developed H.264 AVC (Advanced Video Coding), the video compression standard superior to the existing MPEG-4 Part 2 and H.263 standards, and have developed HEVC (High Efficiency Video Coding) in earnest since 2010. In a similar manner to the existing video compression technology, Test Model under Consideration (TMuC) divides an image into blocks and performs entropy encoding by frequency-transforming and quantizing a residual block by motion estimation or intra prediction. The TMuC of the HEVC performs motion estimation by using multiple reference frames, encodes reference frame indexes and motion vectors as motion information, and outputs a bitstream.
The TMuC of the HEVC efficiently encodes motion information by using a merging method. A known merging method generates a set of motion information candidates composed of N pieces of merge direction motion information from decoded adjacent image blocks so as to encode motion information of a current block. When identical motion information with the current motion information exists in the motion information candidate set, merge flag information is designated as “unmerged”. On the other hand, when the identical motion information with the current motion information exists in the motion information candidate set, merge flag information is designated as “merged”, and merge direction information is designated to represent the identical motion information in the motion information candidate set.
Even though the merge flag information is “merged”, the merge direction information is not designated when all pieces of motion information of the motion information candidate set are equal to one another. The merge flag information is output to a bitstream, and current motion information is output to the bitstream when the merge flag is “unmerged”. That is, when the merge flag is “merged” and all pieces of the motion information of the motion information candidate set are equal to one another, the merge direction information is not output to the bitstream. Otherwise, the merge direction information is output to the bitstream. Specifically, the TMuC of the HEVC configures the motion information candidate set as motion information of a block including a sample located just above the leftmost upper sample of the current block and motion information of a block including a sample located on the immediate left side. The inventor(s), however, has experienced that the motion information merge by the above-described method encodes the merge flag with respect to all cases so that efficient encoding becomes difficult.
The inventor(s), therefore, has noted that there is a need for a video encoding and decoding method that can efficiently encode and decode the motion information by deciding whether to encode the motion information by merging, based on pre-encoded information, when performing encoding by merging the motion information.